That's... kinda vague honestly
Fundamentals are still pretty vague & understudied. here is a short version: The 1920s were a period when multiple technical and demographic trends hit tipping points and there was a high degree of volatility in labor movement, capitol movement, and related items.
The US hit the 50% point when the decline in agriculture labor and rural residence became minorities, and movement to urban residence/labor hit is maximum speed. This was occurring in Germany about the same time. In some areas like the British Isles it had occurred sooner, in others like Russia it was still some decades ahead.
Energy technology was near the tipping point between coal predominance & replacement by oil.
Transport was shifting with increasing speed from mature technologies, rail and water, to automotive.
Radio & telephone were starting to replace print and telegraph in key sectors.
Heres the thing; Maturing or mature technologies are less volatile in terms of cash flow, capitol usage, and labor. New technologies are more volatile, with startups failing, labor use unstable, and cash flow less predictable. Mature technologies/industries have a safer or more predictable return on investment, but have declining returns. As industries mature they expand slower & have a small requirement for high return investment capitol. So there is a understandable trend to seek investment in higher return businesses, leading to riskier investment in new poorly understood sectors. On the labor side this is reflected in labor being shut out of mature industries and attempting to find a place in new, where the skills are different and workers enter at a lower skill level at less pay.
In the 1920s more than the usual number of economic sectors had hit the maturity/startup or transition phase in the same decade or two. The result was a above average or even extreme level of volatility across investment and labor in broad segments of the economy.